I think Tristar, it was Duty Pay (an hourly rate whilst on duty) that was introduced to pay for inflight food.
Sector pay is a set amount per sector, not hourly, which I believe is paid so that those who fly more sectors than other pilots are recompensed in some way.
It is generally acknowledged that a 4 sector day, with short sectors and minimal turnarounds is a harder day than a single long sector flight equating to the same duty time. Hence the 4 sector day would attract a higher rate of pay.
PP